3 files changed, 64 insertions, 30 deletions

diff --git a/fs/ramfs/file-nommu.c b/fs/ramfs/file-nommu.c
index 266531343aae..1739a4aba25f 100644
--- a/fs/ramfs/file-nommu.c
+++ b/fs/ramfs/file-nommu.c
@@ -123,35 +123,6 @@ add_error:
 
 /*****************************************************************************/
 /*
- * check that file shrinkage doesn't leave any VMAs dangling in midair
- */
-static int ramfs_nommu_check_mappings(struct inode *inode,
-                                      size_t newsize, size_t size)
-{
-        struct vm_area_struct *vma;
-        struct prio_tree_iter iter;
-
-        down_write(&nommu_region_sem);
-
-        /* search for VMAs that fall within the dead zone */
-        vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap,
-                              newsize >> PAGE_SHIFT,
-                              (size + PAGE_SIZE - 1) >> PAGE_SHIFT
-                              ) {
-                /* found one - only interested if it's shared out of the page
-                 * cache */
-                if (vma->vm_flags & VM_SHARED) {
-                        up_write(&nommu_region_sem);
-                        return -ETXTBSY; /* not quite true, but near enough */
-                }
-        }
-
-        up_write(&nommu_region_sem);
-        return 0;
-}
-
-/*****************************************************************************/
-/*
  *
  */
 static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
@@ -169,7 +140,7 @@ static int ramfs_nommu_resize(struct inode *inode, loff_t newsize, loff_t size)
 
         /* check that a decrease in size doesn't cut off any shared mappings */
         if (newsize < size) {
-                ret = ramfs_nommu_check_mappings(inode, newsize, size);
+                ret = nommu_shrink_inode_mappings(inode, size, newsize);
                 if (ret < 0)
                         return ret;
         }
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 2265f28eb47a..60c467bfbabd 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1089,6 +1089,7 @@ extern void zone_pcp_update(struct zone *zone);
 
 /* nommu.c */
 extern atomic_long_t mmap_pages_allocated;
+extern int nommu_shrink_inode_mappings(struct inode *, size_t, size_t);
 
 /* prio_tree.c */
 void vma_prio_tree_add(struct vm_area_struct *, struct vm_area_struct *old);
diff --git a/mm/nommu.c b/mm/nommu.c
index 32be0cf51ba6..48a2ecfaf059 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -1914,3 +1914,65 @@ int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, in
         mmput(mm);
         return len;
 }
+
+/**
+ * nommu_shrink_inode_mappings - Shrink the shared mappings on an inode
+ * @inode: The inode to check
+ * @size: The current filesize of the inode
+ * @newsize: The proposed filesize of the inode
+ *
+ * Check the shared mappings on an inode on behalf of a shrinking truncate to
+ * make sure that that any outstanding VMAs aren't broken and then shrink the
+ * vm_regions that extend that beyond so that do_mmap_pgoff() doesn't
+ * automatically grant mappings that are too large.
+ */
+int nommu_shrink_inode_mappings(struct inode *inode, size_t size,
+                                size_t newsize)
+{
+        struct vm_area_struct *vma;
+        struct prio_tree_iter iter;
+        struct vm_region *region;
+        pgoff_t low, high;
+        size_t r_size, r_top;
+
+        low = newsize >> PAGE_SHIFT;
+        high = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
+
+        down_write(&nommu_region_sem);
+
+        /* search for VMAs that fall within the dead zone */
+        vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap,
+                              low, high) {
+                /* found one - only interested if it's shared out of the page
+                 * cache */
+                if (vma->vm_flags & VM_SHARED) {
+                        up_write(&nommu_region_sem);
+                        return -ETXTBSY; /* not quite true, but near enough */
+                }
+        }
+
+        /* reduce any regions that overlap the dead zone - if in existence,
+         * these will be pointed to by VMAs that don't overlap the dead zone
+         *
+         * we don't check for any regions that start beyond the EOF as there
+         * shouldn't be any
+         */
+        vma_prio_tree_foreach(vma, &iter, &inode->i_mapping->i_mmap,
+                              0, ULONG_MAX) {
+                if (!(vma->vm_flags & VM_SHARED))
+                        continue;
+
+                region = vma->vm_region;
+                r_size = region->vm_top - region->vm_start;
+                r_top = (region->vm_pgoff << PAGE_SHIFT) + r_size;
+
+                if (r_top > newsize) {
+                        region->vm_top -= r_top - newsize;
+                        if (region->vm_end > region->vm_top)
+                                region->vm_end = region->vm_top;
+                }
+        }
+
+        up_write(&nommu_region_sem);
+        return 0;
+}